Patent GB-854904-A (GB)
Title: Flight aid systems for aircraft
IPC: B64D45/00
Filed: 1957-01-01
Abstract: 854,904. Aircraft flight aid systems. SPERRY RAND CORPORATION. Jan. 1, 1957 [Jan. 3, 1956], No. 69/57. Class 40 (1). An aircraft flight aid system comprises means  for supplying a signal representing a desired heading change, means connected thereto for producing control signals representing required changes in roll attitude and yaw rate, and means for continuously varying the relative  magnitudes of the two control signals in accordance with the airspeed of the craft. The system is particularly applicable to a helicopter for presenting in a single instrument the information necessary for the pilot to adjust the three controls (Fig. 1) when making a turn or changing altitude. The cyclic rotor blade pitch stick 11 controls the pitch and roll attitudes, the anti-torque propeller pedal bar 12 the yaw, and the collective rotor blade pitch stick 13 the altitude. Fore-and-aft and lateral motions are a function of the position of the cyclic stick 11. The system is shown diagrammatically in Fig. 1, where the various input signals are correlated as shown and applied to four pointers in a single instrument 15. The pointers 16 and 17 are of the conventional type representing deviations of the pitch and roll attitudes from those necessary to effect a given turn, and by the present system their deflections show to the pilot how much adjustment of the cyclic stick 11 is necessary. A further pointer 19 moves relative to indices 20 to show what adjustment of the collective stick 13 is necessary to produce a desired change in altitude. Finally, a marker 21 moves relative to fixed marks 22 to indicate the necessary amount of adjustment of the pedal bar 12 when changing heading. This marker 21 may be of the same appearance as the pointer 19. The pilot adjusts the three controls to restore all the pointers to their zero positions and thus ensures that any turn, ascent or descent will be correctly co-ordinated. In Fig. 2 a vertical gyro 26 provides a roll displacement signal which is mixed with a rate signal at 41 and applied to a meter movement 45 which controls the pointer 17. This signal is further modified by a preset control 42 to allow for gyro mounting errors or load distribution, and also modified in accordance with heading and speed, as described below. A heading rate gyro 50 gives an output which is  modified with an acceleration signal at 51 and applied to a further meter movement 49 for actuating the pedal-bar marker 21. This signal is also modified in accordance with heading and speed, as described below, and can be replaced by a signal representing pedal displacement at 87. Signals from a gyro-magnetic compass 66 are combined in a follow-up synchro 69 with a manually-operated heading selector 68 which operates a mechanical differential 70 and releasable friction-clutch 68<SP>1</SP>. Pointers 64 and 67 show the actual and desired headings, respectively. Heading guidance signals, e.g. from a ground track, are supplied at 104, and modified at 140 if the craft is to be displaced from the track by a predetermined amount. These two heading command signals are each applied to two potentiometers 71, 72 and 97, 98, respectively, where they are modified in accordance with airspeed sensed at 76 and used to modify the signals supplied to control the indicators 17 and 21. The electrical values of the mixing circuits are so chosen that the right amount of co-ordination is achieved at all airspeeds. A biasing resistor 72<SP>1</SP> ensures that a heading reference will be given at maximum airspeed, and a further biasing resistor 97<SP>1</SP> provides for orientating the craft to a ground-track heading at zero airspeed. Pitch displacement signals are obtained from the vertical gyro 26 and mixed with rate signals at 52 to energize a meter movement 54 to operate the cyclic pitch pointer 16. These are modified (a) by a preset control 53 to compensate for gyro and trim errors, (b) by an airspeed selector 94, and (c) from an angle-ofdescent selector 125 and/or glide slope receiver 115 (see below). The airspeed selector 94 operates a potentiometer 92 whose output is compared with that of airspeed-responsive potentiometer 90, and any difference is fed to the meter 54. Altitude signals are obtained from a sensor 57 or (when hovering) from a cable device 102, combined with rate signals at 58 and acceleration signals at 58<SP>1</SP> and applied to a meter movement 59 which operates the pointer 16. As before, the acceleration signal can be replaced by a stick displacement signal from 88. The signals are modified by a preset compensating control and by angle-of-descent signals as in the case of the pitch signals. In addition, command signals can be fed in from an altitude selector 57 and a hold-off control via switch 103. Ascent or descent at a fixed rate can be achieved by switching in a biasing signal from source 100, and at any predetermined rate by passing the signals through a potentiometer 101 set by a knob 125. When a desired altitude is approached (as set by control 57), the switches 1011 and 103 are put in the " A " positions and the craft will level off gradually as the altitude error signal tends to zero. The craft can also be manoeuvred to follow a glide-slope signal from a receiver 115, this being combined with a rate signal at 1191 and applied to a transformer 120 from which two outputs of opposite phases are obtained, one being applied to the channel of the collective pitch pointer 19 and the other to the channel of the cyclic pitch pointer 16. The relative amounts of these two outputs are adjusted by the manual selector 125, which also varies the speed signal at 129 so that the pilot is automatically advised to adjust whichever control will have the greatest effect at the particular airspeed. At the same time " interlocks " 130 and 1301 are switched in according to the particular flight plan selected (not shown) to set particular values of the speed and altitude command signals. If it is desired to approach through a secondary lobe of the glide slope path (making a higher angle with the horizontal) the pilot passes through a number of maxima of the beam centres by observing the deflections of the pointers 16 and 19 without responding to them, until the desired lobe is reached. The appearance of the instrument dial under various conditions is displayed in Figs. 3-10 (not shown), and the corresponding operation of the controls is described. The modifccations of Figs. 11-16 (not shown), describe alternative ways of combining the signals, wherein the airspeed varies the gains of variable amplifiers through which the roll angle, yaw rate, heading error and radio beam displacement signals pass. The arrangement of the various limiters is different in some cases. In Fig. 15 also, the airspeed signal is applied to an E-type transformer whose core is moved by the heading-rate gyro. In a further modification (Fig. 17, not shown) the angle-ofdescent circuit is provided with a manual control to allow for head or tail winds. Specifications 854,905, 854,906 and 854,907 are referred to.